Transmission/reception method for MTC apparatus

ABSTRACT

A method for receiving a signal of a first physical downlink shared channel (PDSCH), includes receiving first information specifying a plurality of subframes used for the wireless device, determining multiple downlink subframes, to receive a signal of a first PDSCH, based on the plurality of subframes specified in the first information, receiving the signal of the first PDSCH which is repeated over the determined multiple downlink subframes and based on that the signal of the first PDSCH includes a first system information block (SIB), determining that a signal of a second PDSCH including a data other than the first SIB is not transmitted in the determined multiple downlink subframes, wherein the first SIB is dedicated for the wireless device and different from a SIB for a user equipment (UE) used by a user.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/906,964 filed on Jan. 22, 2016 (now U.S. Pat. No. 10,375,529 issuedon Aug. 6, 2019), which was filed as the National Phase of PCTInternational Application No. PCT/KR2014/005950, filed on Jul. 3, 2014,which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalApplication No. 61/858,629, filed on Jul. 26, 2013, and to U.S.Provisional Application No. 61/866,551, filed on Aug. 16, 2013, all ofthese applications are hereby expressly, incorporated by reference intothe present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to mobile communication.

Description of the Related Art

3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) thatis an advancement of UMTS (Universal Mobile Telecommunication System) isbeing introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonalfrequency division multiple access) is used for downlink, and SC-FDMA(single carrier-frequency division multiple access) is used for uplink.The 3GPP LTE adopts MIMO (multiple input multiple output) having maximumfour antennas. Recently, a discussion of 3GPP LTE-A (LTE-Advanced) whichis the evolution of the 3GPP LTE is in progress.

As set forth in 3GPP TS 36. 211 V10. 4. 0, the physical channels in 3GPPLTE may be classified into data channels such as PDSCH (physicaldownlink shared channel) and PUSCH (physical uplink shared channel) andcontrol channels such as PDCCH (physical downlink control channel),PCFICH (physical control format indicator channel), PHICH (physicalhybrid-ARQ indicator channel) and PUCCH (physical uplink controlchannel).

Meanwhile, in recent years, communication, i.e., machine typecommunication (MTC), occurring between devices or between a device and aserver without a human interaction, i.e., a human intervention, isactively under research. The MTC refers to the concept of communicationbased on an existing wireless communication network used by a machinedevice instead of a user equipment (UE) used by a user.

Since the MTC has a feature different from that of a normal UE, aservice optimized to the MTC may differ from a service optimized tohuman-to-human communication. In comparison with a current mobilenetwork communication service, the MTC can be characterized as adifferent market scenario, data communication, less costs and efforts, apotentially great number of MTC apparatuses, wide service areas, lowtraffic for each MTC apparatus, etc.

Recently, it is considered to extend cell coverage of a BS for an MTCapparatus, and various schemes for extending the cell coverage are underdiscussion. However, when the cell coverage is extended, if the BStransmits a channel to the MTC apparatus located in the coverageextension region as if transmitting a channel to a normal UE, the MTCapparatus has a difficulty in receiving the channel.

Further, as the MTC apparatus is expected to have low performance inorder to supply more MTC apparatuses at a low price, if the BS transmitsa PDCCH or a PDSCH to the MTC apparatus located in the coverageextension region as if transmitting a PDCCH or a PDSCH to a normal UE,the MTC apparatus has a difficulty in receiving the PDCCH or the PDSCH.

SUMMARY OF THE INVENTION

Accordingly, the disclosure of the specification has been made in aneffort to solve the problem.

To achieve the foregoing purpose, when a machine-type (MTC) apparatus islocated in a coverage extension region of a base station (BS), the BSmay repeatedly transmit PDCCHs or PDSCHs (that is, transmit a bundle ofPDCCHs or PDSCHs) on a plurality of subframes.

However, to repeatedly transmit PDCCHs to the MTC apparatus located inthe coverage extension region on a plurality of subframes in thepresence of an existing UE in a cell, a very large quantity of resourcesmay be used, causing damage to the existing UE.

To solve such a problem, an embodiment of the present invention providesa transmission and reception method performed by a machine-typecommunication (MTC) apparatus. The method may comprise: receiving, bythe MTC apparatus, configuration information on a multicast-broadcastsingle-frequency network (MBSFN) subframe from a base station;receiving, by the MTC apparatus, downlink data for the MTC apparatus ona data region of the MBSFN subframe; and receiving, by the MTCapparatus, a cell-specific reference signal (CRS) only on a portion ofresource blocks (RBs) of an entire system bandwidth in the data regionof the MBSFN subframe. The CRS received only on the portion of RBs istransmitted while electric power is increased by the base station.

The method may further comprise: recognizing, by the MTC apparatus, theMBSFN subframe as a subframe dedicated for MTC.

The method may further comprise: receiving, by the MTC apparatus, aphysical downlink control channel (PDCCH) comprising schedulinginformation of the downlink data for the MTC apparatus on a controlregion of the MBSFN subframe.

The method may further comprise: receiving, by the MTC apparatus, thedownlink data for the MTC apparatus also in a data region of a generalsubframe other than the MBSFN subframe.

To solve the foregoing problem, an embodiment of the present inventionprovides a transmission and reception method performed by a basestation. The method may comprise: transmitting, by the base station,configuration information on a multicast-broadcast single-frequencynetwork (MBSFN) subframe; scheduling, by the base station, a radioresource for a general user equipment on a general subframe other thanthe MBSFN subframe, and scheduling a radio resource for a machine-typecommunication (MTC) apparatus on the general subframe and the MBSFNsubframe; transmitting, by the base station, a cell-specific referencesignal (CRS) on an entire system bandwidth in a control region of theMBSFN subframe, and transmitting a CRS only on a portion of resourceblocks (RBs) of an entire system bandwidth in a data region. The CRS onthe portion of RBs is transmitted while electric power is increased.

The method may further comprise: transmitting, by the base station,downlink control information comprising scheduling information ondownlink data for the MTC apparatus on the control region of the MBSFNsubframe; and transmitting, by the base station, the downlink data forthe MTC apparatus on the data region of the MBSFN subframe.

Further, to solve the foregoing problem, an embodiment of the presentinvention provides a machine-type communication (MTC) apparatus. The MTCapparatus may comprise: a processor; a transceiver controlled by theprocessor to receive configuration information on a multicast-broadcastsingle-frequency network (MBSFN) subframe from a base station, toreceive downlink data for the MTC apparatus on a data region of theMBSFN subframe according to the configuration information, and toreceive a cell-specific reference signal (CRS) only on a portion ofresource blocks (RBs) of an entire system bandwidth in the data regionof the MBSFN subframe. The CRS received only on the portion of RBs istransmitted while electric power is increased by the base station.

In addition, to solve the foregoing problem, an embodiment of thepresent invention provides a base station. The base station maycomprise: a transceiver to transmit configuration information on amulticast-broadcast single-frequency network (MBSFN) subframe; and aprocessor to schedule a radio resource for a general user equipment on ageneral subframe other than the MBSFN subframe, and to schedule a radioresource for a machine-type communication (MTC) apparatus on the generalsubframe and the MBSFN subframe. The transceiver transmits acell-specific reference signal (CRS) on an entire system bandwidth in acontrol region of the MBSFN subframe, and transmits a CRS only on aportion of resource blocks (RBs) of an entire system bandwidth in a dataregion, transmitting the CRS on the portion of RBs while electric poweris increased.

According to the disclosure of the present specification, the problem ofthe foregoing conventional technology is solved. More specifically,according to the disclosure of the present specification, the receptionperformance and decoding performance of a machine-type communication(MTC) apparatus located in a coverage extension region of a base stationmay be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication system.

FIG. 2 illustrates the architecture of a radio frame according tofrequency division duplex (FDD) of 3rd generation partnership project(3GPP) long term evolution (LTE).

FIG. 3 illustrates the architecture of a downlink radio frame accordingto time division duplex (TDD) in 3GPP LTE.

FIG. 4 illustrates an example resource grid for one uplink or downlinkslot in 3GPP LTE.

FIG. 5 illustrates the architecture of a downlink subframe.

FIG. 6 illustrates the architecture of an uplink subframe in 3GPP LTE.

FIG. 7 illustrates an example of comparison between a single carriersystem and a carrier aggregation system.

FIG. 8 exemplifies cross-carrier scheduling in a carrier aggregationsystem.

FIG. 9 illustrates an example of transmitting system information.

FIG. 10A illustrates an example of machine-type communication (MTC).

FIG. 10B illustrates an example of cell coverage extension for an MTCapparatus.

FIG. 11 illustrates an example of a subframe for an MTC apparatuslocated in a coverage extension region to receive downlink data.

FIG. 12 illustrates an example of a region where a CRS for an MTCapparatus located in a coverage extension region is transmitted.

FIG. 13 illustrates an example of a region where a PDSCH for an MTCapparatus located in a coverage extension region is transmitted.

FIGS. 14A and 14B illustrate an example of repeatedly transmitting abundle of PBCHs for an MTC apparatus located in a coverage extensionregion.

FIG. 15 illustrates an example of a resource for transmitting a CRS.

FIG. 16 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the specification includes themeaning of the plural number unless the meaning of the singular numberis definitely different from that of the plural number in the context.In the following description, the term ‘include’ or ‘have’ may representthe existence of a feature, a number, a step, an operation, a component,a part or the combination thereof described in the specification, andmay not exclude the existence or addition of another feature, anothernumber, another step, another operation, another component, another partor the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, user equipment (UE) may be stationary or mobile, and maybe denoted by other terms such as device, wireless device, terminal, MS(mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

FIG. 1 shows a wireless communication system.

Referring to FIG. 1, the wireless communication system includes at leastone base station (BS) 20. Respective BSs 20 provide a communicationservice to particular geographical areas 20 a, 20 b, and 20 c (which aregenerally called cells).

The UE generally belongs to one cell and the cell to which the terminalbelong is referred to as a serving cell. A base station that providesthe communication service to the serving cell is referred to as aserving BS. Since the wireless communication system is a cellularsystem, another cell that neighbors to the serving cell is present.Another cell which neighbors to the serving cell is referred to aneighbor cell. A base station that provides the communication service tothe neighbor cell is referred to as a neighbor BS. The serving cell andthe neighbor cell are relatively decided based on the UE.

Hereinafter, a downlink means communication from the base station 20 tothe terminal 10 and an uplink means communication from the terminal 10to the base station 20. In the downlink, a transmitter may be a part ofthe base station 20 and a receiver may be a part of the terminal 10. Inthe uplink, the transmitter may be a part of the terminal 10 and thereceiver may be a part of the base station 20.

Meanwhile, the wireless communication system may be any one of amultiple-input multiple-output (MIMO) system, a multiple-inputsingle-output (MISO) system, a single-input single-output (SISO) system,and a single-input multiple-output (SIMO) system. The MIMO system uses aplurality of transmit antennas and a plurality of receive antennas. TheMISO system uses a plurality of transmit antennas and one receiveantenna. The SISO system uses one transmit antenna and one receiveantenna. The SIMO system uses one transmit antenna and one receiveantenna. Hereinafter, the transmit antenna means a physical or logicalantenna used to transmit one signal or stream and the receive antennameans a physical or logical antenna used to receive one signal orstream.

Meanwhile, the wireless communication system may be generally dividedinto a frequency division duplex (FDD) type and a time division duplex(TDD) type. According to the FDD type, uplink transmission and downlinktransmission are achieved while occupying different frequency bands.According to the TDD type, the uplink transmission and the downlinktransmission are achieved at different time while occupying the samefrequency band. A channel response of the TDD type is substantiallyreciprocal. This means that a downlink channel response and an uplinkchannel response are approximately the same as each other in a givenfrequency area. Accordingly, in the TDD based wireless communicationsystem, the downlink channel response may be acquired from the uplinkchannel response. In the TDD type, since an entire frequency band istime-divided in the uplink transmission and the downlink transmission,the downlink transmission by the base station and the uplinktransmission by the terminal may not be performed simultaneously. In theTDD system in which the uplink transmission and the downlinktransmission are divided by the unit of a subframe, the uplinktransmission and the downlink transmission are performed in differentsubframes.

Hereinafter, the LTE system will be described in detail.

FIG. 2 shows a downlink radio frame structure according to FDD of 3rdgeneration partnership project (3GPP) long term evolution (LTE).

The radio frame of FIG. 2 may be found in the section 5 of 3GPP TS 36.211 V10. 4. 0 (2011-12) “Evolved Universal Terrestrial Radio Access(E-UTRA); Physical Channels and Modulation (Release 10)”.

Referring to FIG. 2, the radio frame consists of 10 subframes. Onesubframe consists of two slots. Slots included in the radio frame arenumbered with slot numbers 0 to 19. A time required to transmit onesubframe is defined as a transmission time interval (TTI). The TTI maybe a scheduling unit for data transmission. For example, one radio framemay have a length of 10 milliseconds (ms), one subframe may have alength of 1 ms, and one slot may have a length of 0. 5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of subframes included in the radio frame or the numberof slots included in the subframe may change variously.

Meanwhile, one slot may include a plurality of OFDM symbols. The numberof OFDM symbols included in one slot may vary depending on a cyclicprefix (CP).

FIG. 3 shows an example of a resource grid for one uplink or downlinkslot in 3GPP LTE.

For this, 3GPP TS 36. 211 V10. 4. 0 (2011-12) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, Ch. 4 may be referenced, and this is for TDD (timedivision duplex).

The radio frame includes 10 sub-frames indexed 0 to 9. One sub-frameincludes two consecutive slots. The time for one sub-frame to betransmitted is denoted TTI (transmission time interval). For example,the length of one sub-frame may be 1 ms, and the length of one slot maybe 0.5 ms.

One slot may include a plurality of OFDM (orthogonal frequency divisionmultiplexing) symbols in the time domain. The OFDM symbol is merely torepresent one symbol period in the time domain since 3GPP LTE adoptsOFDMA (orthogonal frequency division multiple access) for downlink (DL),and thus, the multiple access scheme or name is not limited thereto. Forexample, OFDM symbol may be denoted by other terms such as SC-FDMA(single carrier-frequency division multiple access) symbol or symbolperiod.

By way of example, one slot includes seven OFDM symbols. However, thenumber of OFDM symbols included in one slot may vary depending on thelength of CP (cyclic prefix). According to 3GPP TS 36. 211 V8. 7. 0, oneslot, in the normal CP, includes seven OFDM symbols, and in the extendedCP, includes six OFDM symbols.

Resource block (RB) is a resource allocation unit and includes aplurality of sub-carriers in one slot. For example, if one slot includesseven OFDM symbols in the time domain and the resource block includes 12sub-carriers in the frequency domain, one resource block may include7×12 resource elements (REs).

Sub-frames having index #1 and index #6 are denoted special sub-frames,and include a DwPTS (Downlink Pilot Time Slot: DwPTS), a GP (GuardPeriod) and an UpPTS (Uplink Pilot Time Slot). The DwPTS is used forinitial cell search, synchronization, or channel estimation in aterminal. The UpPTS is used for channel estimation in the base stationand for establishing uplink transmission sync of the terminal. The GP isa period for removing interference that arises on uplink due to amulti-path delay of a downlink signal between uplink and downlink.

In TDD, a DL (downlink) sub-frame and a UL (Uplink) co-exist in oneradio frame. Table 1 shows an example of configuration of a radio frame.

TABLE 1 UL-DL Switch- Con- point Subframe index figuration periodicity 01 2 3 4 5 6 7 8 9 0  5 ms D S U U U D S U U U 1  5 ms D S U U D D S U UD 2  5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S UU D D D D D D 5 10 ms D S U D D D D D D D 6  5 ms D S U U U D S U U D

Here, ‘D’ denotes a DL sub-frame, ‘U’ a UL sub-frame, and ‘S’ a specialsub-frame. When receiving a UL-DL configuration from the base station,the terminal may be aware of whether a sub-frame is a DL sub-frame or aUL sub-frame according to the configuration of the radio frame.

The DL (downlink) sub-frame is split into a control region and a dataregion in the time domain. The control region includes up to three firstOFDM symbols in the first slot of the sub-frame. However, the number ofOFDM symbols included in the control region may be changed. A PDCCH andother control channels are assigned to the control region, and a PDSCHis assigned to the data region.

FIG. 4 illustrates an example resource grid for one uplink or downlinkslot in 3GPP LTE.

Referring to FIG. 4, the uplink slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand NRB resource blocks (RBs) in the frequency domain. For example, inthe LTE system, the number of resource blocks (RBs), i.e., NRB, may beone from 6 to 110.

Here, by way of example, one resource block includes 7×12 resourceelements that consist of seven OFDM symbols in the time domain and 12sub-carriers in the frequency domain. However, the number ofsub-carriers in the resource block and the number of OFDM symbols arenot limited thereto. The number of OFDM symbols in the resource block orthe number of sub-carriers may be changed variously. In other words, thenumber of OFDM symbols may be varied depending on the above-describedlength of CP. In particular, 3GPP LTE defines one slot as having sevenOFDM symbols in the case of CP and six OFDM symbols in the case ofextended CP.

OFDM symbol is to represent one symbol period, and depending on system,may also be denoted SC-FDMA symbol, OFDM symbol, or symbol period. Theresource block is a unit of resource allocation and includes a pluralityof sub-carriers in the frequency domain. The number of resource blocksincluded in the uplink slot, i.e., NUL, is dependent upon an uplinktransmission bandwidth set in a cell. Each element on the resource gridis denoted resource element.

Meanwhile, the number of sub-carriers in one OFDM symbol may be one of128, 256, 512, 1024, 1536, and 2048.

In 3GPP LTE, the resource grid for one uplink slot shown in FIG. 4 mayalso apply to the resource grid for the downlink slot.

FIG. 5 illustrates the architecture of a downlink sub-frame.

In FIG. 5, assuming the normal CP, one slot includes seven OFDM symbols,by way of example. However, the number of OFDM symbols included in oneslot may vary depending on the length of CP (cyclic prefix). That is, asdescribed above, according to 3GPP TS 36. 211 V10. 4. 0, one slotincludes seven OFDM symbols in the normal CP and six OFDM symbols in theextended CP.

Resource block (RB) is a unit for resource allocation and includes aplurality of sub-carriers in one slot. For example, if one slot includesseven OFDM symbols in the time domain and the resource block includes 12sub-carriers in the frequency domain, one resource block may include7×12 resource elements (REs).

The DL (downlink) sub-frame is split into a control region and a dataregion in the time domain. The control region includes up to first threeOFDM symbols in the first slot of the sub-frame. However, the number ofOFDM symbols included in the control region may be changed. A PDCCH(physical downlink control channel) and other control channels areassigned to the control region, and a PDSCH is assigned to the dataregion.

The physical channels in 3GPP LTE may be classified into data channelssuch as PDSCH (physical downlink shared channel) and PUSCH (physicaluplink shared channel) and control channels such as PDCCH (physicaldownlink control channel), PCFICH (physical control format indicatorchannel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH(physical uplink control channel).

The PCFICH transmitted in the first OFDM symbol of the sub-frame carriesCIF (control format indicator) regarding the number (i.e., size of thecontrol region) of OFDM symbols used for transmission of controlchannels in the sub-frame. The wireless device first receives the CIF onthe PCFICH and then monitors the PDCCH.

Unlike the PDCCH, the PCFICH is transmitted through a fixed PCFICHresource in the sub-frame without using blind decoding.

The PHICH carries an ACK (positive-acknowledgement)/NACK(negative-acknowledgement) signal for a UL HARQ (hybrid automatic repeatrequest). The ACK/NACK signal for UL (uplink) data on the PUSCHtransmitted by the wireless device is sent on the PHICH.

The PBCH (physical broadcast channel) is transmitted in the first fourOFDM symbols in the second slot of the first sub-frame of the radioframe. The PBCH carries system information necessary for the wirelessdevice to communicate with the base station, and the system informationtransmitted through the PBCH is denoted MIB (master information block).In comparison, system information transmitted on the PDSCH indicated bythe PDCCH is denoted SIB (system information block).

The PDCCH may carry activation of VoIP (voice over internet protocol)and a set of transmission power control commands for individual UEs insome UE group, resource allocation of an higher layer control messagesuch as a random access response transmitted on the PDSCH, systeminformation on DL-SCH, paging information on PCH, resource allocationinformation of UL-SCH (uplink shared channel), and resource allocationand transmission format of DL-SCH (downlink-shared channel). A pluralityof PDCCHs may be sent in the control region, and the terminal maymonitor the plurality of PDCCHs. The PDCCH is transmitted on one CCE(control channel element) or aggregation of some consecutive CCEs. TheCCE is a logical allocation unit used for providing a coding rate perradio channel's state to the PDCCH. The CCE corresponds to a pluralityof resource element groups. Depending on the relationship between thenumber of CCEs and coding rates provided by the CCEs, the format of thePDCCH and the possible number of PDCCHs are determined.

The control information transmitted through the PDCCH is denoteddownlink control information (DCI). The DCI may include resourceallocation of PDSCH (this is also referred to as DL (downlink) grant),resource allocation of PUSCH (this is also referred to as UL (uplink)grant), a set of transmission power control commands for individual UEsin some UE group, and/or activation of VoIP (Voice over InternetProtocol).

The base station determines a PDCCH format according to the DCI to besent to the terminal and adds a CRC (cyclic redundancy check) to controlinformation. The CRC is masked with a unique identifier (RNTI; radionetwork temporary identifier) depending on the owner or purpose of thePDCCH. In case the PDCCH is for a specific terminal, the terminal'sunique identifier, such as C-RNTI (cell-RNTI), may be masked to the CRC.Or, if the PDCCH is for a paging message, a paging indicator, forexample, P-RNTI (paging-RNTI) may be masked to the CRC. If the PDCCH isfor a system information block (SIB), a system information identifier,SI-RNTI (system information-RNTI), may be masked to the CRC. In order toindicate a random access response that is a response to the terminal'stransmission of a random access preamble, an RA-RNTI (randomaccess-RNTI) may be masked to the CRC.

In 3GPP LTE, blind decoding is used for detecting a PDCCH. The blinddecoding is a scheme of identifying whether a PDCCH is its own controlchannel by demasking a desired identifier to the CRC (cyclic redundancycheck) of a received PDCCH (this is referred to as candidate PDCCH) andchecking a CRC error. The base station determines a PDCCH formataccording to the DCI to be sent to the wireless device, then adds a CRCto the DCI, and masks a unique identifier (this is referred to as RNTI(radio network temporary identifier) to the CRC depending on the owneror purpose of the PDCCH.

The uplink channels include a PUSCH, a PUCCH, an SRS (Sounding ReferenceSignal), and a PRACH (physical random access channel).

FIG. 6 illustrates the architecture of an uplink sub-frame in 3GPP LTE.

Referring to FIG. 6, the uplink sub-frame may be separated into acontrol region and a data region in the frequency domain. The controlregion is assigned a PUCCH (physical uplink control channel) fortransmission of uplink control information. The data region is assigneda PUSCH (physical uplink shared channel) for transmission of data (insome cases, control information may also be transmitted).

The PUCCH for one terminal is assigned in resource block (RB) pair inthe sub-frame. The resource blocks in the resource block pair take updifferent sub-carriers in each of the first and second slots. Thefrequency occupied by the resource blocks in the resource block pairassigned to the PUCCH is varied with respect to a slot boundary. This isreferred to as the RB pair assigned to the PUCCH having beenfrequency-hopped at the slot boundary.

The terminal may obtain a frequency diversity gain by transmittinguplink control information through different sub-carriers over time. mis a location index that indicates a logical frequency domain locationof a resource block pair assigned to the PUCCH in the sub-frame.

The uplink control information transmitted on the PUCCH includes an HARQ(hybrid automatic repeat request), an ACK (acknowledgement)/NACK(non-acknowledgement), a CQI (channel quality indicator) indicating adownlink channel state, and an SR (scheduling request) that is an uplinkradio resource allocation request.

The PUSCH is mapped with a UL-SCH that is a transport channel. Theuplink data transmitted on the PUSCH may be a transport block that is adata block for the UL-SCH transmitted for the TTI. The transport blockmay be user information. Or, the uplink data may be multiplexed data.The multiplexed data may be data obtained by multiplexing the transportblock for the UL-SCH and control information. For example, the controlinformation multiplexed with the data may include a CQI, a PMI(precoding matrix indicator), an HARQ, and an RI (rank indicator). Or,the uplink data may consist only of control information.

A carrier aggregation system is now described.

FIG. 7 illustrates an example of comparison between a single carriersystem and a carrier aggregation system.

Referring to FIG. 7, there may be various carrier bandwidths, and onecarrier is assigned to the terminal. On the contrary, in the carrieraggregation (CA) system, a plurality of component carriers (DL CC A toC, UL CC A to C) may be assigned to the terminal. Component carrier (CC)means the carrier used in then carrier aggregation system and may bebriefly referred as carrier. For example, three 20 MHz componentcarriers may be assigned so as to allocate a 60 MHz bandwidth to theterminal.

Carrier aggregation systems may be classified into a contiguous carrieraggregation system in which aggregated carriers are contiguous and anon-contiguous carrier aggregation system in which aggregated carriersare spaced apart from each other. Hereinafter, when simply referring toa carrier aggregation system, it should be understood as including boththe case where the component carrier is contiguous and the case wherethe control channel is non-contiguous.

When one or more component carriers are aggregated, the componentcarriers may use the bandwidth adopted in the existing system forbackward compatibility with the existing system. For example, the 3GPPLTE system supports bandwidths of 1. 4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHzand 20 MHz, and the 3GPP LTE-A system may configure a broad band of 20MHz or more only using the bandwidths of the 3GPP LTE system. Or, ratherthan using the bandwidths of the existing system, new bandwidths may bedefined to configure a wide band.

The system frequency band of a wireless communication system isseparated into a plurality of carrier frequencies. Here, the carrierfrequency means the cell frequency of a cell. Hereinafter, the cell maymean a downlink frequency resource and an uplink frequency resource. Or,the cell may refer to a combination of a downlink frequency resource andan optional uplink frequency resource. Further, in the general casewhere carrier aggregation (CA) is not in consideration, one cell mayalways have a pair of an uplink frequency resource and a downlinkfrequency resource.

In order for packet data to be transmitted/received through a specificcell, the terminal should first complete a configuration on the specificcell. Here, the configuration means that reception of system informationnecessary for data transmission/reception on a cell is complete. Forexample, the configuration may include an overall process of receivingcommon physical layer parameters or MAC (media access control) layersnecessary for data transmission and reception or parameters necessaryfor a specific operation in the RRC layer. A configuration-complete cellis in the state where, once when receiving information indicating packetdata may be transmitted, packet transmission and reception may beimmediately possible.

The cell that is in the configuration complete state may be left in anactivation or deactivation state. Here, the “activation” means that datatransmission or reception is being conducted or is in ready state. Theterminal may monitor or receive a control channel (PDCCH) and a datachannel (PDSCH) of the activated cell in order to identify resources(possibly frequency or time) assigned thereto.

The “deactivation” means that transmission or reception of traffic datais impossible while measurement or transmission/reception of minimalinformation is possible. The terminal may receive system information(SI) necessary for receiving packets from the deactivated cell. Incontrast, the terminal does not monitor or receive a control channel(PDCCH) and data channel (PDSCH) of the deactivated cell in order toidentify resources (probably frequency or time) assigned thereto.

Cells may be classified into primary cells and secondary cells, servingcells.

The primary cell means a cell operating at a primary frequency. Theprimary cell is a cell where the terminal conducts an initial connectionestablishment procedure or connection re-establishment procedure withthe base station or is a cell designated as a primary cell during thecourse of handover.

The secondary cell means a cell operating at a secondary frequency. Thesecondary cell is configured once an RRC connection is established andis used to provide an additional radio resource.

The serving cell is configured as a primary cell in case no carrieraggregation is configured or when the terminal cannot offer carrieraggregation. In case carrier aggregation is configured, the term“serving cell” denotes a cell configured to the terminal and a pluralityof serving cells may be included. One serving cell may consist of onedownlink component carrier or a pair of {downlink component carrier,uplink component carrier}. A plurality of serving cells may consist of aprimary cell and one or more of all the secondary cells.

As described above, the carrier aggregation system, unlike the singlecarrier system, may support a plurality of component carriers (CCs),i.e., a plurality of serving cells.

Such carrier aggregation system may support cross-carrier scheduling.The cross-carrier scheduling is a scheduling scheme that may conductresource allocation of a PUSCH transmitted through other componentcarriers than the component carrier basically linked to a specificcomponent carrier and/or resource allocation of a PDSCH transmittedthrough other component carriers through a PDCCH transmitted through thespecific component carrier. In other words, the PDCCH and the PDSCH maybe transmitted through different downlink CCs, and the PUSCH may betransmitted through an uplink CC other than the uplink CC linked to thedownlink CC where the PDCCH including a UL grant is transmitted. Assuch, the system supporting cross-carrier scheduling needs a carrierindicator indicating a DL CC/UL CC through which a PDSCH/PUSCH istransmitted where the PDCCH offers control information. The fieldincluding such carrier indicator is hereinafter denoted carrierindication field (CIF).

The carrier aggregation system supporting cross-carrier scheduling maycontain a carrier indication field (CIF) in the conventional DCI(downlink control information) format. In the cross-carrierscheduling-supportive carrier aggregation system, for example, an LTE-Asystem, may have 3 bits expanded due to addition of the CIF to theexisting DCI format (i.e., the DCI format used in the LTE system), andthe PDCCH architecture may reuse the existing coding method or resourceallocation method (i.e., CCE-based resource mapping).

FIG. 8 exemplifies cross-carrier scheduling in the carrier aggregationsystem.

Referring to FIG. 8, the base station may configure a PDCCH monitoringDL CC (monitoring CC) set. The PDCCH monitoring DL CC set consists ofsome of all of the aggregated DL CCs, and if cross-carrier scheduling isconfigured, the user equipment performs PDCCH monitoring/decoding onlyon the DL CCs included in the PDCCH monitoring DL CC set. In otherwords, the base station transmits a PDCCH for PDSCH/PUSCH that issubject to scheduling only through the DL CCs included in the PDCCHmonitoring DL CC set. The PDCCH monitoring DL CC set may be configuredUE-specifically, UE group-specifically, or cell-specifically.

FIG. 8 illustrates an example in which three DL CCs (DL CC A, DL CC B,and DL CC C) are aggregated, and DL CC A is set as a PDCCH monitoring DLCC. The user equipment may receive a DL grant for the PDSCH of DL CC A,DL CC B, and DL CC C through the PDCCH of DL CC A. The DCI transmittedthrough the PDCCH of DL CC A contains a CIF so that it may indicatewhich DL CC the DCI is for.

FIG. 9 illustrates an example of transmitting system information.

System information is classified into a master information block (MIB)and a plurality of system information blocks (SIB). The MIB includes themost important physical layer information on a cell. The SIBs includesdifferent types. A first type of SIB includes information used toevaluate whether a UE is allowed to access a cell and schedulinginformation on another type of SIB. A second type of SIB (SIB type 2)includes information on common and shared channels. A third type of SIB(SIB type 3) includes cell reselection information related mostly to aserving cell. A fourth type of SIB (SIB type 4) includes frequencyinformation on a serving cell and intra-frequency information on aneighbor cell related to cell reselection. A fifth type of SIB (SIB type5) includes information on another E-UTRA frequency and inter-frequencyinformation on a neighbor cell related to cell reselection. A sixth typeof SIB (SIB type 6) includes information on a UTRA frequency andinformation on a UTRA neighbor cell related to cell reselection. Aseventh type of SIB (SIB type 7) includes information on a GERANfrequency related to cell reselection.

As shown in FIG. 9, the MIB is transmitted to a UE 10 via a PBCH. Thefirst type of SIB (SIB type 1) is mapped to a DL-SCH and transmitted tothe UE 10 via a PDSCH. Other types of SIBs are transmitted to the UE viaa PDSCH through a system information message.

Hereinafter, MTC will be described.

FIG. 10A illustrates an example of machine type communication (MTC).

The MTC refers to information exchange performed between MTC apparatuses100 via a BS 200 without human interactions or information exchangeperformed between the MTC apparatus 100 and an MTC server 700 via theBS.

The MTC server 700 is an entity for communicating with the MTC apparatus100. The MTC server 700 executes an MTC application, and provides anMTC-specific service to the MTC apparatus.

The MTC apparatus 100 is a wireless device for providing the MTC, andmay be fixed or mobile.

A service provided using the MTC is differentiated from an existingcommunication service requiring human intervention, and its servicerange is various, such as tracking, metering, payment, medical fieldservices, remote controlling, etc. More specifically, examples of theservice provided using the MTC may include reading a meter, measuring awater level, utilizing a surveillance camera, inventory reporting of avending machine, etc.

The MTC apparatus is characterized in that a transmission data amount issmall and uplink/downlink data transmission/reception occurs sometimes.Therefore, it is effective to decrease a unit cost of the MTC apparatusand to decrease battery consumption according to a low data transmissionrate. The MTC apparatus is characterized of having a small mobility, andthus is characterized in that a channel environment does almost notchange.

FIG. 10B illustrates an example of cell coverage extension for an MTCapparatus.

Recently, it is considered to extend cell coverage of a BS for an MTCapparatus 100, and various schemes for extending the cell coverage areunder discussion.

However, when the cell coverage is extended, if the BS transmits a PDSCHand a PDCCH including scheduling information for the PDSCH to the MTCapparatus located in the coverage extension region as if it istransmitted to a normal UE, the MTC apparatus has a difficulty inreceiving them.

Embodiments of the Present Invention

Thus, embodiments of the present invention are provided to solve theforegoing problem.

According to an embodiment of the present invention, to solve theforegoing problem, when a BS transmits a PDSCH and PDCCH to an MTCapparatus located in a coverage extension region, the BS repeatedlytransmits the PDSCH and PDCCH on a plurality of subframes (for example,a bundle of subframes). Thus, the MTC apparatus receives a bundle ofPDCCHs through the plurality of subframes and decode the bundle ofPDCCHs, thereby increasing decoding success rate. That is, a PDCCH maybe successfully decoded using a portion or all of the PDCCHs in thebundle received through a plurality of subframes. Likewise, the MTCapparatus receives a bundle of PDSCHs through a plurality of subframesand decodes a portion or all of PDSCHs in the bundle, thereby increasingdecoding success rate.

Similarly, the MTC apparatus located in the coverage extension regionmay transmit a bundle of PUCCHs through a plurality of subframes. Also,the MTC apparatus may transmit a bundle of PUSCHs through a plurality ofsubframes.

However, to repeatedly transmit PDSCHs and PDCCHs to the MTC apparatuslocated in the coverage extension region on a plurality of subframes inthe presence of an existing UE in a cell, a very large quantity ofresources may be used, causing damage to the existing UE.

Thus, a solution to such a problem will be described below. Hereinafter,for convenience of description, an MTC apparatus located in a coverageextension region is referred to as a coverage enhancement (CE) MTCapparatus, and an MTC apparatus located out of the coverage extensionregion as a non-CE MTC apparatus.

According to an embodiment of the present invention to overcome theforegoing problem, time division multiplexing (TDM) may be used suchthat a CE MTC apparatus and a non-CE MTC apparatus alternately operatein a time-divided manner in order to prevent an operation of a BS forthe CE MTC apparatus from causing damage to an existing UE or the non-CEMTC apparatus. TDM may be a based on a long-term period in tens ofminutes or a short-tem period in subframes.

Here, according to an embodiment, the BS in a cell may transmit downlinkdata to the CE MTC apparatus on a multicast-broadcast single-frequencynetwork (MBSFN) subframe and transmit downlink data to the non-CE MTCapparatus on a general subframe (that is, non-MBSFN subframe) other thanthe MBSFN subframe.

Hereinafter, embodiments of the present invention will be described indetail.

(A) Subframes for CE MTC Apparatus

As shown in FIG. 11, a 10-msec radio frame may be divided into MBSFNsubframes and non-MBSFN subframes. Generally, an MTC apparatus or UE mayreceive an SIB from a BS in a cell to identify the positions of MBSFNsubframes of the cell.

Defining a subframe for the BS in the cell to transmit downlink data toa CE MTC apparatus as a CE MTC subframe, the CE MTC subframe may alwaysbe the same as an MBSFN subframe for the BS in the cell to provide anexisting normal UE with a service. Thus, when the CE MTC apparatusobtains information on the position of an MBSFN subframe from the BS,the MBSFN subframe may be assumed as a CE MTC subframe. The CE MTCsubframe may include not only the MBSFN subframe but also a non-MBSFNsubframe or may include non-MBSFN subframes only.

Meanwhile, the CE MTC apparatus may also receive a control channel/datachannel and a reference signal (RS) on a non-MBSFN subframe, and alsoadditionally on a CE MTC subframe. Specifically, the CE MTC apparatusmay receive a cell-specific or cell-common control channel/data channelon a non-MBSFN subframe and receive a UE-specific control channel/datachannel on a CE MTC subframe (or MBSFN subframe). Here, as describedabove, when the CE MTC subframe includes the non-MBSFN subframes only,the CE MTC apparatus may receive an individual UE-specific controlchannel/data channel on the non-MBSFN subframes.

Meanwhile, according to an embodiment, in order that the serving cell ofthe CE MTC apparatus can also support Multimedia Broadcast MulticastServices (MBMS), CE MTC subframes may include all or a portion of MBSFNsubframes. For example, as shown in FIG. 11, MBSFN subframes may includesubframes 1, 2, 3, 6, 7, and 8, while CE MTC subframes for the CE MTCapparatus to receive data may include subframes 1, 2, 6, and 7 only.

In this case, the BS of the cell may notify the existing normal UE orthe CE MTC apparatus which subframes among the MBSFN subframes are usedas CE MTC subframes, separately from the positions of the MBSFNsubframes. Information on the positions of the CE MTC subframes may betransmitted to the CE MTC apparatus through an MIB or SIB. Here, theinformation on the positions of the CE MTC subframes may be representedin a 10-bit bitmap format indicating subframes used as the CE MTCsubframes among 10 subframes in the 10-msec radio frame. Alternatively,the information on the positions of the CE MTC subframes may berepresented in an M-bit bitmap format indicating subframes used as theCE MTC subframes among M MBSFN subframes in the 10-msec radio frame.

As such, even when a subframe region for transmitting downlink data forthe CE MTC apparatus includes all or a portion of the MBSFN subframes,the MTC apparatus may assume that the positions of the CE MTC subframesare the same as the positions of the MBSFN subframes until the BSnotifies the MTC apparatus of the positions of the CE MTC subframes.Alternatively, the MTC apparatus may assume that the CE MTC subframesincluding all or a portion of the MBSFN subframe are always in a fixedsubframe region.

Thus, the CE MTC apparatus may use all or a portion of the MBSFNsubframes as CE MTC subframes only in the presence of one or more MBSFNsubframes assigned by the BS.

(B) Transmission of Downlink Data on CE MTC Subframe

When a BS of a cell transmits downlink data for a CE MTC apparatus onall or a portion of MBSFN subframes, a general PDSCH or EPDCCH may betransmitted on the corresponding MBSFN subframes, other than a physicalmulticast channel (PMCH) on a non-

When the BS of the cell transmits the downlink data for the CE MTCapparatus on all or a portion of the MBSFN subframes, a PDCCH may betransmitted only on up to two OFDM symbols as in the MBSFN subframeseven though a PDSCH may be transmitted on all available OFDM symbols inthe corresponding MBSFN subframes. This is because an existing normal UErecognizes the corresponding subframes as general MBSFN subframes andthus recognizes that the BS of the cell transmits the PDCCH only on upto two OFDMs in the corresponding subframes.

Furthermore, when the BS of the cell transmits the downlink data for theCE MTC apparatus on all or a portion of the MBSFN subframes, a normal CPor extended CP is available in the entire symbol region of thecorresponding subframes as in a non-MBSFN subframe.

In addition, when the BS of the cell transmits the downlink data for theCE MTC apparatus on all or a portion of the MBSFN subframes, not anMBSFN RS but a CRS may be transmitted in the corresponding subframes asin a non-MBSFN subframe.

Also, when the BS of the cell transmits the downlink data for the CE MTCapparatus on all or a portion of the MBSFN subframes, a separatetransmission mode (TM) from a TM used for a non-MBSFN subframe may beused for the corresponding subframes. Here, TM2 may always be used asthe TM used for the CE MTC subframes. Alternatively, the BS may notifythe MTC apparatus of the TM used for the CE MTC subframes through anMIB, an SIB, or the like.

(C) Transmission of CRS on CE MTC Subframe

When a BS of a cell transmits downlink data for a CE MTC apparatus onall or a portion of MBSFN subframes, a CRS transmitted on thesesubframes may have a different form from that of a CRS transmitted on ageneral downlink subframe. That is, when the CE MTC apparatus isassigned one or more MBSFN subframes or a set of MBSFN subframes by theBS, the CE MTC apparatus may assume that the CRS is transmitted from theBS of the cell in the assigned subframes and frequency/sub-band. The CEMTC apparatus capable of making this assumption may not support aparticular TM performing demodulation with a DM-RS, for example, TM8,TM9, and TM10.

Meanwhile, a current LTE-A system considers a technique of improvingchannel estimation performance of a normal UE by performing transmissionpower boosting of a CRS. For transmission power boosting of a CRS, a CRSis not transmitted in a portion of REs or RBs where a CRS isconventionally transmitted but a remaining CRS may be transmitted withgreater power.

In an embodiment, by using this technique, the BS may transmit a CRSonly in a portion of physical resource blocks (PRBs) in the entiresystem band, that is, all PRBs, on CE MTC subframes including all or aportion of MBSFN subframes. Specifically, techniques of transmitting aCRS only in a portion of PRBs on CE MTC subframes including all or aportion of MBSFN subframes may be as follows in i to iii.

i) A CRS may be transmitted only on six intermediate PRBs in the entiresystem band. Specifically, the CRS may be transmitted only on sixintermediate PRBs or a designated sub-band on CE MTC subframes includingall or a portion of MBSFN subframes. Here, the CRS may be transmittedwith boosted power. More specifically, transmission power for the CRSmay be boosted by the number of all PRBs in the system band/the numberof PRBs in the sub-band times as compared with conventional transmissionpower.

ii) Defining the number of PRBs in the system band as PRB_S, a CRS maybe transmitted only on ½*PRB_S intermediate PRBs. Specifically, the CRSmay be transmitted only on six intermediate PRBs in CE MTC subframesincluding all or a portion of MBSFN subframes. Here, the CRS may betransmitted with boosted power. Specifically, transmission power for theCRS may be boosted by two times as compared with conventionaltransmission power.

iii) A CRS may be transmitted only through even-numbered or odd-numberedPRBs. More specifically, the CRS may be transmitted only oneven-numbered or odd-numbered PRBs in CE MTC subframes including all ora portion of MBSFN subframes. Here, the CRS may be transmitted withboosted power. Specifically, transmission power for the CRS may beboosted by two times as compared with conventional transmission power.

According to the foregoing techniques, a CRS is not transmitted on allREs in a PRB set not to transmit a CRS. Instead, zero power transmissionmay be performed or a PDCCH/EPDCCH/PDSCH may be transmitted on an REposition in the PRB originally for transmitting a CRS. That is, aPDCCH/EPDCCH/PDSCH may be transmitted or zero power transmission may beperformed in the position for transmitting a CRS. More specifically,zero power transmission may be performed in a position for transmittinga CRS in an OFDM symbol/PRB region where a PDCCH or EPDCCH istransmitted. Alternatively, a PDSCH may be transmitted via rate-matchingin a position originally for transmitting a CRS in an OFDM symbol/PRBregion where a PDSCH is transmitted. To protect an existing UE,transmission power boosting for a CRS may be performed in REs other thanthe PDCCH region. For example, it may be assumed that a CRS istransmitted as conventionally transmitted in the entire system bandwidthon first three OFDM symbols and a CRS is transmitted with presetincreased power in other regions. It may be assumed that when thistechnique is used, the existing UE does not perform QAM transmission.Thus, it is not needed to separately set a power ratio of a PDSCH to aCRS. When a non-MBSFN subframe is assigned for the CE MTC apparatus andtransmission power is increased as mentioned above, the BS sets, for theexisting UE, this subframe as an MBSFN subframe so that the existing UEmay not receive a CRS transmitted by the BS with boosted power. That is,for the existing UE, it may be assumed that transmission power boostingfor a CRS occurs only on an MBSFN subframe or an existing UE-DRXsubframe. A detailed description will be made with reference to FIG. 12.

As shown in FIG. 12, a CRS may be transmitted in the entire systembandwidth, as conventionally transmitted, in a PDCCH region on CE MTCsubframes including all or a portion of subframes, and a CRS may betransmitted only in a portion of PRBs in the entire system band only inan OFDM symbol region where a PDSCH/EPDCCH for the CE MTC apparatus istransmitted. When the CRS is transmitted only in the portion of the PRBson the OFDM symbols where the PDSCH/EPDCCH is transmitted, the sametechniques as mentioned above may be applied.

(D) Transmission of Cell-Specific Data on Subframe for CE MTC Apparatus

When a BS transmits downlink data for a CE MTC apparatus on all or aportion of MBSFN subframes, cell-specific or cell-common data (forexample, the first type of SIB and the second type of SIB) for the CEMTC apparatus may also be transmitted on the CE MTC subframes. In thiscase, the BS may transmit the cell-specific or cell-common data usingtwo methods. According to a first method, the BS may transmit thecell-specific or cell-common data for the CE MTC apparatus separatelyfrom cell-specific or cell-common for an existing UE. To this end, theBS may use different RNTIs. According to a second method, the BS maytransmit the cell-specific or cell-common data for the existing UE usinga general method, and repeatedly transmit the cell-specific orcell-common data for a CE MTC apparatus located in a coverage extensionregion through subframes set for the CE MTC apparatus.

According to the above two methods, the CE MTC apparatus needs to assumethat the first type of SIB can be received on CE MTC subframes as aportion of subframes conventionally known not to receive the first typeof SIB through.

Assuming that the cell-specific or cell-common data is transmitted inthe CE MTC subframes, the MTC apparatus may assume that thecell-specific or cell-common data is received always on a particularsubframe among the CE MTC subframes. For example, when six subframes ina 10-msec radio frame are set as CE MTC subframes, it may be assumedthat a cell-specific PDSCH is always received on a first subframe amongthe six frames.

Alternatively, the MTC apparatus may assume that the first type of SIBis received always on a particular subframe of the CE MTC subframes.When particular subframes for receiving cell-specific data are a subsetof the CE MTC subframes, only the subframes may be used as a PDCCH forthe cell-specific data and/or a bundle of PDSCHs including thecell-specific data. More specifically, when a set of the subframes isdetermined, it may be assumed that a PDCCH including schedulinginformation on user-specific data or a PDSCH including user-specificdata may not be transmitted on the subframes.

Meanwhile, when the BS transmits the downlink data for the CE MTCapparatus on all or a portion of MBSFN subframes, only a UE-specificsearch space (USS) may always be included in a (E) PDCCH transmitted onthe subframes. That is, the CE MTC apparatus may assume that only theUSS is present in the CE MTC subframes and thus only user-specific datamay be received on the subframes set for the CE MTC apparatus. In thiscase, the CE MTC apparatus may receive cell-specific or cell-common dataonly on subframes for the existing UE. In addition, the MTC apparatusmay assume that only a CSS is received on a non-MBSFN subframe.

(E) Transmission of PDSCH on CE MTC Subframe

When a BS transmits downlink data for a CE MTC apparatus on all or aportion of MBSFN subframes, a PRB region for transmitting a PDSCH amongPRBs in the subframes may be different from a PRB region fortransmitting a PDSCH on a general downlink subframe.

As shown in FIG. 13, the BS may transmit a PDSCH for the CE MTCapparatus only through a portion of the entire downlink systembandwidth. For example, a PDSCH bandwidth may have a size a half timesthe size of the entire system bandwidth. In this case, a PRB region fortransmitting a PDSCH may be a PRB region as large as a central PDSCHband. When the PDSCH is transmitted in the PRB region, the PDSCH may betransmitted with greater power than transmitted in a non-MBSFN subframe.For example, a PDSCH may be transmitted with two times greater power perRE on a CE MTC subframe than a PDSCH on a non-MBSFN subframe.

(F) Transmission of ACK/NACK of CE MTC Subframe

Hereinafter, suppose a situation where when CE MTC subframes are alwaysthe same as MBSFN subframes or are all or a portion of the MBSFNsubframes, a CE MTC apparatus receives a user-specific controlchannel/data channel only on the CE MTC subframes (or MBSFN subframes).

Here, when ND CE MTC subframes are present in a 10-msec radio frame, thepositions of the CE MTC subframes may be represented by Di. Here, i maybe 0, 1, . . . , ND. Here, the positions of subframes for the CE MTCapparatus to transmit an ACK/NACK of a user-specific data channel may bedetermined according to the positions of CE MTC subframes for receivinga user-specific data channel in each 10-msec radio frame.

In FDD, the position of a subframe for the CE MTC to transmit anACK/NACK may be Di+4.

In TDD, defining the number of subframes for the CE MTC apparatus totransmit an ACK/NACK in each 10-msec radio frame as NA, the position ofthe subframes for the CE MTC apparatus to transmit an ACK/NACK in the10-msec radio frame may be determined as (Di+Gi) mod 10. Here, i may be0, 1, . . . , ND. Gi for determining the positions of subframes for a CEMTC UE to transmit an ACK/NACK according to the position of the CE MTCsubframe may be determined as follows in Table 2. Table 2 illustrates Giaccording to the position Di of a CE MTC subframe in each TDD UL-DLconfiguration.

TABLE 2 Di UL-DL configuration 0 1 2 3 4 5 6 7 8 9 0 4 6 — — — 4 6 — — —1 7 6 — — 4 7 6 — — 4 2 7 6 — 4 8 7 6 — 4 8 3 4 11 — — — 7 6 6 5 5 4 1211 — — 8 7 7 6 5 4 5 12 11 — 9 8 7 6 5 4 13  6 7 7 — — — 7 7 — — 5

For example, when TDD UL-DL configuration 2 shown in Table 1 is used andthe positions of CE MTC subframes are 3, 4, 8, and 9, the position of asubframe for the CE MTC apparatus to transmit an ACK/NACK may becalculated as follows. First, the positions of the CE MTC subframes maybe expressed as D1=3, D2=4, D3=8, and D4=9. Since UL-DL configuration 2is used, Gi is obtained from Table 2 such that G1=4, G2=8, G3=4, andG4=8. The positions of subframes for transmitting an ACK/NACK are(D1+G1) mod 10=7, (D2+G2) mod 10=2, (D3+G3) mod 10=2, and (D4+G4) mod10=7. Accordingly, the positions of subframes for the CE MTC apparatusto transmit an ACK/NACK are subframe 2 and subframe 7. Thus, the MTCapparatus may repeatedly transmit an ACK/NACK through subframe 2 andsubframe 7 from a subframe for starting to transmit an ACK/NACK afterreception of PDSCHs is finished.

There may be another method for transmitting ACK/NACK information on abundle of PDSCHs on a plurality of subframes after the CE MTC apparatusreceives the bundle of PDSCHs on CE MTC subframes in the TDDenvironment. Specifically, when the CE MTC apparatus finishes receivingthe bundle of PDSCHs in ‘subframe n,’ the CE MTC apparatus may transmitan ACK/NACK on a plurality of subframes (that is, NA subframes) from‘subframe n+G.’ More specifically, the CE MTC apparatus may transmit anACK/NACK of the PDSCHs on ‘subframes n+G*a.’ Here, a may be 0, 1, . . ., NA. Here, G may be determined according to Table 2. G and D correspondto Gi and Di in Table 2, respectively.

(G) PUSCH Transmission Subframe Corresponding to CE MTC Subframe

Hereinafter, suppose a situation where when CE MTC subframes are alwaysthe same as MBSFN subframes or are all or a portion of the MBSFNsubframes, a CE MTC apparatus receives a user-specific controlchannel/data channel only on the CE MTC subframes (or MBSFN subframes).

Here, when ND CE MTC subframes are present in a 10-msec radio frame, thepositions of the CE MTC subframes may be represented by Di. Here, i maybe 0, 1, . . . , ND. Here, the positions of subframes for the CE MTCapparatus to transmit a PUSCH may be determined according to thepositions of CE MTC subframes for receiving a user-specific controlchannel in each 10-msec radio frame.

In FDD, the position of a subframe for the CE MTC to transmit a PUSCHmay be Di+4.

In TDD, defining the number of subframes for the CE MTC apparatus totransmit a PUSCH in each 10-msec radio frame as NU, the position of asubframe for the CE MTC apparatus to transmit a PUSCH in each 10-msecradio frame may be determined as (Di+Ki) mod 10. Here, i may be 0, 1, .. . , ND.

Ki may be determined according to Table 3. Table 3 illustrates Kiaccording to the position of a CE MTC subframe Di in each UL-DLconfiguration.

TABLE 3 TDD Di UL-DL configuration 0 1 2 3 4 5 6 7 8 9 0 4 6 4 6 1 6 4 64 2 4 4 3 4 4 4 4 4 4 5 4 6 7 7 7 7 5

However, when a subframe Di for receiving an uplink grant from the BS isnot a subframe illustrated in Table 4 but a different subframe, the MTCapparatus may exclude the subframe in determining a subframe fortransmitting a PUSCH.

TABLE 4 TDD UL-DL configuration Subframe for receiving uplink grant 0 0,1, 5, 6 1 1, 4, 6, 9 2 3, 8 3 0, 8, 9 4 8, 9 5 8 6 0, 1, 5, 6, 9

For example, when TDD UL-DL configuration 1 is used and the positions ofCE MTC subframes are 1, 4, and 6, the position of a subframe fortransmitting a PUSCH may be calculated as follows. First, the positionsof the CE MTC subframes may be expressed as D1=1, D2=4, and D3=6. SinceUL-DL configuration 1 is used, Ki is obtained from Table 3 such thatK1=6, K2=4, and K3=6. The positions of subframes for transmitting aPUSCH are (C1+K1) mod 10=7, (C2+K2) mod 10=8, and (C3+K3) mod 10=2.Accordingly, the positions of subframes for the CE MTC apparatus totransmit a PUSCH after receiving a PDCCH including an uplink grant aresubframes 2, 7, and 8. Consequently, a bundle of PUSCHs are transmittedon subframes 2, 7, and 8.

(H) Transmission of PBCH on CE MTC Subframe

A BS may also repeatedly transmit a PBCH for a CE MTC apparatus on aplurality of subframes, which will be described in detail with referenceto FIG. 14.

As shown in FIG. 14A, an existing PBCH is transmitted on subframes 0,10, 20, and 30 for 40 msec, while a bundle of PBCHs repeatedlytransmitted on a plurality of subframes according to an embodiment ofthe present invention may be transmitted on all of the subframes for 40msec. As such, an existing PBCH is transmitted once for 10 msec, whilethe embodiment may transmit a bundle of PBCHs on a plurality ofsubframes for an MTC apparatus located in a coverage extension region.

However, considering the resource region of an existing normal UE or thelike, as shown in FIG. 14B, a PBCH may be repeatedly transmitted only ona portion of subframes in a 10-msec radio frame.

Here, subframes for transmitting a bundle of PBCHs for the CE MTCapparatus, for example, subframes 0, 2, 3, 6, 7, and 8 in FIG. 14B, maybe the same as CE MTC subframes as a subframe region for transmittingdownlink data for the CE MTC. Alternatively, subframes for transmittinga bundle of PBCHs for a CE MTC UE except for subframe 0, for example,subframes 2, 3, 6, 7, and 8 in FIG. 14B, may be the same as CE MTCsubframes as a subframe region for transmitting downlink data for the CEMTC apparatus. Alternatively, a bundle of PBCHs for the CE MTC apparatusexcept for a PBCH transmitted on subframe 0 may be transmitted only onall or a portion of MBSFN subframes.

Here, although the BS of a particular cell uses two or more antennaports, the CE MTC UE does not need high data transmission rate oroperates in a low SNR region and thus may not have good channelestimation performance enough to use two or more RS antenna ports.Further, since the MTC apparatus has low portability and thus may have achannel environment with a considerably low diversity. Thus, it may beinefficient for the BS of the cell to transmit data to the MTC using aplurality of antenna ports.

Thus, according to the embodiment, regardless of the number of antennaports used for an existing PBCH and CRS transmitted through subframe 0,the number of antennas used to transmit a bundle of additional PBCHs forthe CE MTC apparatus may not be increased but be reduced in a resourceregion for transmitting the bundle of additional PBCHs (that is,subframes or CE MTC subframes for transmitting the bundle of PBCHs).More specifically, regardless of the number of antenna ports used for anexisting PBCH and CRS transmitted on subframe 0, only one antenna portmay be used to transmit a bundle of additional PBCHs for the CE MTCapparatus and a CRS in a resource region for transmitting the bundle ofadditional PBCHs for the CE MTC apparatus (that is, subframes or CE MTCsubframes for transmitting the bundle of PBCHs). Here, the antenna portmay be antenna port 0.

Further, according to the embodiment, regardless of the number ofantenna ports used for an existing PBCH and CRS transmitted throughsubframe 0, the number of antenna ports used to transmit a PDSCH and CRSto the CE MTC apparatus on a CE MTC subframe (or in a time/frequencyresource region for transmitting a PDSCH for the CE MTC apparatus) maybe limited. Specifically, regardless of the number of antenna ports usedfor an existing PBCH and CRS transmitted on subframe 0, only one antennaport may be used to transmit a PDSCH and CRS to the CE MTC apparatus ona CE MTC subframe. Here, the antenna port may be antenna port 0.

Great-performance channel estimation is a very important element for aMTC apparatus located in a coverage extension region. One method forimproving channel estimation performance of such an MTC apparatus isenhancing the density of RSs used for channel estimation.

To this end, according to the embodiment, regardless of the number ofantenna ports used for an existing PBCH and CRS, the number of antennaports used to transmit a bundle of additional PBCHs and/or a PDSCH onlyfor the CE MTC apparatus in a subframe (for example, CE MTC subframe) orin a time/frequency resource region for transmitting the bundle ofadditional PBCHs and/or the PDSCH may be limited. Specifically, it issuggested to transmit, through antenna ports used to transmit a bundleof PBCHs and/or data for the CE MTC apparatus, a CRS transmitted throughother antenna ports than antenna ports for transmitting the bundle ofadditional PBCHs and/or a PDSCH for the CE MTC apparatus among antennaports used to transmit an existing PBCH and CRS.

For example, when existing PBCHs and CRSs are transmitted throughantenna ports 0, 1, 2, and 3 and only antenna port 0 is used to transmita bundle of additional PBCHs and/or PDSCHs for the CE MTC apparatus in aCE MTC subframe or a time/frequency resource region for transmitting thebundle of additional PCBHs and/or PDSCHs for the CE MTC apparatus, it issuggested to transmit, through antenna port 0, a CRS which needtransmitting through antenna ports 1, 2, and 3, which will be describedin detail with reference to FIG. 15.

FIG. 15 illustrates an example of a resource for transmitting a CRS.

In (a) and (b) of FIG. 15, numbers indicated in REs represent antennaport numbers. (a) of FIG. 15 illustrates an example of transmitting aCRS on a radio resource grid using a normal CP, and (b) of FIG. 15illustrates an example of transmitting a CRS on a radio resource gridusing an extended CP. As shown in (a) and (b) of FIG. 15, when anexisting CRS is transmitted on REs represented by antenna ports 0, 1, 2,and 3, a CRS which needs transmitting on REs represented by antennaports 0, 1, 2, and 3 may be transmitted using antenna port 0 in a CE MTCsubframe or a time/frequency resource region for transmitting a bundleof additional PBCHs and/or PDSCHs for the CE MTC apparatus. In thiscase, the number of REs for CRSs transmitted on antenna port 0 isincreased. Further, in the corresponding region, only antenna port 0 maybe used to transmit a bundle of PBCHs and/or PDSCHs to the CE MTCapparatus.

The aforementioned embodiments of the present invention can beimplemented through various means. For example, the embodiments of thepresent invention can be implemented in hardware, firmware, software,combination of them, etc. Details thereof will be described withreference to the drawing.

FIG. 16 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the present invention.

The base station (BS) 200/300 includes processor 201/301, memory202/302, and radio frequency (RF) unit 203/303. The memory 202/302coupled with the processor 201/301 stores a variety of information fordriving the processor 201/301. The RF unit 203/303 coupled to theprocessor 201/301 transmits and/or receive radio signals. The processor201/301 implements the proposed functions, procedures, and/or methods.In the aforementioned embodiment, an operation of the BS may beimplemented by the processor 201/301.

The MTC apparatus 100 includes a processor 101, a memory 102, and an RFunit 103. The memory 102 coupled to the processor 101 stores a varietyof information for driving the processor 101. The RF unit 103 coupled tothe processor 101 transmits and/or receives a radio signal. Theprocessor 101 implements the proposed functions, procedure, and/ormethods.

The processor may include an application-specific integrated circuit(ASIC), a separate chipset, a logic circuit, and/or a data processingunit. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orother equivalent storage devices. The RF unit may include a base-bandcircuit for processing a radio signal. When the embodiment isimplemented in software, the aforementioned methods can be implementedwith a module (i.e., process, function, etc.) for performing theaforementioned functions. The module may be stored in the memory and maybe performed by the processor. The memory may be located inside oroutside the processor, and may be coupled to the processor by usingvarious well-known means.

Although the aforementioned exemplary system has been described on thebasis of a flowchart in which steps or blocks are listed in sequence,the steps of the present invention are not limited to a certain order.Therefore, a certain step may be performed in a different step or in adifferent order or concurrently with respect to that described above.Further, it will be understood by those ordinary skilled in the art thatthe steps of the flowcharts are not exclusive. Rather, another step maybe included therein or one or more steps may be deleted within the scopeof the present invention.

What is claimed is:
 1. A method for receiving a signal of a firstphysical downlink shared channel (PDSCH), the method performed by awireless device and comprising: receiving first information specifying aplurality of subframes used for the wireless device; receiving secondinformation specifying at least one multimedia broadcast multicastservice single frequency network (MBSFN) subframe; determining multipledownlink subframes, to receive a signal of a first PDSCH, based on theplurality of subframes specified in the first information; receiving thesignal of the first PDSCH which is repeated over the determined multipledownlink subframes; and receiving a cell-specific reference signal (CRS)over the determined multiple downlink subframes, wherein when thedetermined multiple downlink subframes include the at least one MBSFNsubframe, one or more resource elements (REs), in the MBSFN subframe,having the same positions as REs available for the CRS in a non-MBSFNsubframe are used for zero-power transmission.
 2. The method of claim 1,wherein the first information is received via a second systeminformation block (SIB) or a higher layer signal.
 3. The method of claim1, wherein the first information is expressed as a bitmap in a secondsystem information block (SIB).
 4. The method of claim 3, wherein thebitmap includes 10 bits.
 5. The method of claim 1, wherein the secondinformation is received via a second system information block (SIB). 6.The method of claim 1, wherein the plurality of subframes specified inthe first information include the at least one MBSFN subframe specifiedin the second information.
 7. The method of claim 1, further comprising:if the signal of the first PDSCH includes a first system informationblock (SIB), determining that a signal of a second PDSCH including adata other than the first SIB is not transmitted in the determinedmultiple downlink subframes, wherein the first SIB is dedicated for thewireless device and different from a SIB for a user equipment (UE) usedby a user.
 8. A wireless device for receiving a signal of a firstphysical downlink shared channel (PDSCH), the wireless devicecomprising: a transceiver; and a processor operatively connected to thetransceiver and configured to: control the transceiver to receive firstinformation specifying a plurality of subframes used for the wirelessdevice; receive second information specifying at least one multimediabroadcast multicast service single frequency network (MBSFN) subframe;determine multiple downlink subframes, to receive the signal of thefirst PDSCH, based on the plurality of subframes specified in the firstinformation; receive the signal of the first PDSCH which is repeatedover the determined multiple downlink subframes; and receive acell-specific reference signal (CRS) over the determined multipledownlink subframes, wherein when the plurality of subframes specified inthe first information include the at least one MBSFN subframe specifiedin the second information, one or more resource elements (REs), in theMBSFN subframe, having the same positions as REs available for the CRSin a non-MBSFN subframe are used for zero-power transmission.
 9. Thewireless device of claim 8, wherein the first information is receivedvia a second system information block (SIB) or a higher layer signal.10. The wireless device of claim 8, wherein the first information isexpressed as a bitmap in a second system information block (SIB). 11.The wireless device of claim 10, wherein the bitmap includes 10 bits.12. The wireless device of claim 8, wherein the second information isreceived via a second system information block (SIB).
 13. The wirelessdevice of claim 8, wherein the plurality of subframes specified in thefirst information include the at least one MBSFN subframe specified inthe second information.
 14. The wireless device of claim 8, wherein theprocessor is further configured to: if the signal of the first PDSCHincludes a first system information block (SIB), determine that a signalof a second PDSCH including a data other than the first SIB is nottransmitted in the determined multiple downlink subframes, wherein thefirst SIB is dedicated for the wireless device and different from a SIBfor a user equipment (UE) used by a user.